Estuaries and inshore sediments are important sinks of hydrophobic organic pollutants. High-resolution sedimentary records are an important tool for inverting the history of human activities and the process of industrial civilization in the surrounding areas (or sources of pollution). However, in the complex depositional environments of estuaries and offshore, the relevant sedimentary records often exhibit a variety of different models.
Sediments in the offshore mud zone of the East China Sea are mainly composed of clay silt, silty clay, and sand-silt-clay. They extend from the mouth of the Yangtze River along the coasts of Zhejiang and Fujian to the southwest, and the northeast-southwest length exceeds 1,000 kilometers. The development of inland shelves limited to depths of 50-60 meters is widest at the mouth of the Yangtze River and narrows to the south. The muddy area can be divided into the north adjacent to the Yangtze River argillaceous area and the south Zhejiang argillaceous muddy area. Sediments in the muddy area of ​​the East China Sea mainly come from the Yangtze River, and about 50% of the Yangtze River suspended matter is captured southwards in the Hangzhou Bay and the Bay Islands, forming a argillaceous sediment outside the estuary, and about 30% into the argillaceous sedimentary region along the coast of Fujian and Zhejiang.
Researchers at the Institute of Geochemistry of the Chinese Academy of Sciences chose a special depositional environment in the mud zone of the Yangtze River Estuary and the Zhejiang-Fujian argillaceous area. According to a comparative study of multiple sedimentary columns, there are usually two types of persistent organic pollutants in the estuarine and offshore environments. The main types of sedimentary records: the first type, sedimentary record types controlled by Dahe River. The sedimentary records mainly occur in estuaries or offshore, and there is often no fixed pattern. The common point is that persistent organic pollutants in the soil in the basin are sediments. The main source of pollutants in the material, therefore, the sediment record reflects the re-migration intensity of residual secondary pollution sources in the soil in the basin.
For example, after pesticides are banned, large-scale soil erosion caused by excessive land development in the Yangtze River Basin will cause the simultaneous increase of HCHs and DDTs content in the nearshore sedimentary column; in the years of large-scale flood disasters in the Yangtze River Basin, the corresponding deposition intervals Abnormal peaks occur in HCHs and DDTs. The second type, sedimentary record type controlled by non-large rivers, the sedimentary record often appears at the end of the fluvial material output. The main feature of this sediment record is that the record of pollutant deposition coincides with the history of the use and discharge of primary pollution sources in the area. From the seemingly chaotic estuarine and offshore sedimentation records, two main types of sedimentary records have been summarized. The results of this study provide relevant research on the persistent pollution of persistent organic pollutants, pollution trends, and migration patterns in coastal offshore environments. Important understanding basis.
The research was jointly funded by the “Outstanding Young Talents Training Program†of the State Key Laboratory of Environmental Geochemistry and the National Natural Science Youth Fund (“Permanent Organic Pollutant Behavior in Sediment Deposit and Migration of Sediments into the Sea of ​​the Yangtze Riverâ€, 41103046). Relevant research results were published in the latest issue of Science of the Total Environment (Volume 539, 1 January 2016, Pages 388–394), with research papers entitled DDTs and HCHs in sediment cores from the coastal East China Sea.
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